It is common for refrigeration units, especially transport refrigeration units, such as refrigeration units associated with trucks, trailers, containers, and the like, to include an internal combustion engine in a prime mover arrangement. The engine, which is usually a diesel engine, is arranged to drive a refrigerant compressor at a selected one of at least first and second operating speeds. The first operating speed, which is higher than the second operating speed, is selected by a set point temperature control algorithm during initial temperature pull down of an associated conditioned space. Thereafter, the second or lower operating speed is utilized to maintain the temperature of the conditioned space in a predetermined temperature range adjacent to the selected set point temperature. The first or higher operating speed is only resorted to during temperature extremes when the lower operating speed is not sufficient to maintain the selected set point temperature.
The air mover arrangements of the refrigeration unit, such as the condenser and evaporator fans or blowers are conventionally operated from the engine, such as by belt and pulley arrangements, and thus the air flow rates depend upon the selected operating speed of the engine, providing a higher air flow rate and velocity during the high speed operating mode than during the low speed operating mode.
This air mover drive arrangement is suitable for the condenser fan, since the condenser is normally rejecting less heat during low speed operation when the conditioned space is close to the set point temperature. The lower operating speed of the evaporator fan or blower, however, may adversely affect temperature uniformity in the conditioned space. This is especially true when the conditioned space does not contain chutes which direct conditioned air to different locations of the conditioned space. Thus, it would be desirable, and it is an object of the present invention, to improve temperature uniformity throughout a conditioned space in refrigeration systems in which a refrigeration unit includes a refrigerant compressor and evaporator fan driven at first and second speeds by a prime mover in response to a set point temperature control algorithm.